The regulation of amino acid metabolism and protein turnover is being investigated in isolated tissues, primarily rat muscles, and in isolated cells and subcellular fractions of rat liver and other tissues. The effect of hormones (insulin, thyroxin, glucocorticoids) and diabetes on the enzymatic degradation of branched chain amino acids is studied, with particilar emphasis on the regulation of the branced chain alpha-keto acid dehydrogenase system in various tissues. The regulation of protein synthesis and degradation is studied in muscles, the effect of hormones, diabetes, amino acids, electrolytes, pH, the cellular redox potential and different energy yielding substrates. The role of the above factors in translational control of muscle protein synthesis is being investigated as well as their effect on the intermediary metabolism of amino acids in muscles.